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Re. 24,243 Reissued Dec. 4, 1956 ALLOYS AND ELECTRICAL RESISTANCEELEMENTS James M. Lohr, Morristown, N. J., assignor to Driver- HarrisCompany, Harrison, N. J., a corporation of New Jersey 8 Claims. (Cl.75-124) atter enclosed in heavy brackets appears in the original patentbut forms no part of this reissue specification; matter printed initalics indicates the additions made by reissue.

This invention relates to alloys and more particularly to alloys forelectric resistance units.

In the manufacture of electrical resistance units, an

alloy having the property of resisting oxidation at high temperature isessential. The alloys forming the subject matter of this invention arecharacterized by ability to resist oxidation and by a prolonged life,exceeding that of other known alloys when used under high temperatureconditions. Since the introduction of nickelchromium-iron alloys aselectric resistance units, many developments have occurred that haveimproved their resistance to oxidation. In a number of prior patents Ihave disclosed and claimed various alloying additions of calcium,zirconium and aluminum which greatly improve the life of heatingelements. It has also been proposed to add rare earth metals, such ascerium, to nickelchromium-iron alloys to improve the life of the heatingelements.

I have found that when calcium as rare earth metals are added to alloys,better results are obtained than if the calcium, zirconium, aluminumgroup or the rare earths are used alone. The present invention is,therefore, directed to the addition of small quantities of the rareearths with calcium and aluminum to nickel-chromium-iron alloys. I havefound that such combination of addition elements greatly increases theperiod of life of nickel-chromiumiron alloys when employed underconditions where they are subjected to high temperatures. The alloysforming the subject matter of the present invention may also containsmall amounts of either silicon or manganese or both of these elements.The rare earth metals may be added as misch metal having an approximatecomposition of 45 percent cerium, 30 percent lanthanum, 20 percentytterbium and didymium. Although it is convenient to add the rare earthmetals in the form of misch metal, I do not restrict myself to the useof this material as one or more of the rare earth metals may be addedsingly and its effect is of a similar nature. The additions may be usedto advantage with the nickel-chromium-iron alloys of which the bestknown examples are the alloys of 30 to 70 percent nickel, 10 to 25percent chromium, balance iron.

This application is a division of my copending application Serial No.117,510, filed September 23, 1949, now Patent No. 2,581,420. The claimsof this application are directed to alloys containing 30 to 50 percentnickel and 10 to 25 percent chromium, and more specifically to alloyscontaining substantially 35 percent nickel and substantially 20 percentchromium.

In the examples hereinafter described, the additions were made to thealloys consisting of substantially 35 perand aluminum as wellnickel-chromium-iron cent nickel, 20 percent chromium and balance iron.Rare earth metals, such as misch metal, with calcium and aluminum may beadded to such alloys with or without silicon. The proportions of nickelin such alloys may vary from 30 to 50 percent and the chromium from 10to 25 percent with the balance iron. Employing nickelchromium-irc-nalloys of these proportions, I have added calcium, aluminum and mischmetal in the quantities or amounts hereinafter mentioned.

In preparing alloys containing the addition elements above mentioned,the quantities of such addition elements are subtracted from the ironcontent. For example, when additions are made to base alloys containing30 to 50 percent nickel, 10 to 25 percent chromium, the final alloyswill contain 30 to 50 percent nickel, 10 to 25 percent chromium, theaddition elements calcium, aluminum and the rare earth metals in thepercentages hereinafter stated, and the balance iron. While. theproportions of calcium, aluminum and rare earth metals may vary withincertain limits, I have found that the best results are obtained whenthese materials are present in the final alloys within thefollowing'limits:

Percent Calcium .O0l.20

Aluminum .01-1.0

Rare earth metals Trace-0.50

If the alloys contain manganese, silicon, or carbon, they may be presentwithin the following limits:

- Percent Manganese .02-4.0

Silicon .203.0

Carbon 0.25 max.

While alloys having the properties desired to a very high degree areobtained within the limits before men tioned, the preferred range ofaddition elements is as follows:

The alloys so prepared have been tested for resistance to oxidation athigh temperature by a modification of the method approved by theAmerican Society for Testing Materials Accelerated Life Test forMetallic Materials, B76-39. In conducting such test, the alloy isproduced in the form of a wire, drawn to a diameter of approximately.025" and tested at a temperature of 1950 F., instead of a temperatureof 2050 R, which is the temperature of the standard ASTM method fortesting the 60 nickel, 15 chromium alloys. The useful life in hours forwire of substantially 35 percent nickel, 20 percent chromium containingcalcium, zirconium and aluminum as addition elements, balance iron, isof the order of hours. The useful life of the alloys of the presentinvention, according to the above described test, is of the order of 400hours. Thus, the useful life is increased around 300 percent over thatof the alloys containing the calcium, zirconium, aluminum group when therare earth metals are added with calcium and aluminum in the proportionsherein stated.

The alloys are prepared in the usual manner by placing the ingredientsin a bath, heating until the alloying elements become molten and thenpouring. In adding rare earth metals to a molten bath, it is necessaryto add considerably larger quantities than will be found in the castmetal because they vaporize readily and pass out of the bath. In manyinstances, with additions of the rare earth metals only a spectrographictrace of one or more of the rare earth metals is found in the castmaterial. The presence of such traces, however, in combination withcalcium and aluminum, greatly increases the oxidation resistance of thealloys. The rare earth metals may be added in amounts suflicient toleave a residue in the cast alloys up to .2 percent but in mostinstances the use of such amounts is not necessary.

In the test referred to above the increase of electrical resistance attemperature with time is plotted and an increase of percent inresistance is known as the useful life. The life of the tested specimento burn-out is known as total life.

I claim:

1. A nickel-chromium-iron alloy consisting substantially of 35 percentnickel, substantially 20 percent chromium, .001 to .20 percent calcium,.01 to 1.0 percent aluminum, a trace to .50 percent of a rare earthmetal, balance essentially iron.

2. A nickel-chromium-iron alloy consisting substantially of 35 percentnickel, substantially 20 percent chromium, .001 to .07 percent calcium,.01 to .40 percent aluminum, a trace to .20 percent of a rare earthmetal, balance essentially iron.

3. A nickel-chromium-iron alloy consisting substantially of 35 percentnickel, substantially 20 percent chromium, .001 to .20 percent calcium,.01 to 1.0 percent aluminum, a trace to .50 percent cerium andlanthanum, balance essentially iron.

4. A nickel-chromium-iron alloy consisting substantially of 35 percentnickel, substantially 20 percent chromium, .001 to .07 percent calcium,.01 to .40 percent aluminum, a trace to .20 percent cerium andlanthanum, balance essentially iron.

. 4 5. An electric resistance element consisting substantially ofpercent nickel, substantially 20 percent chr0- mium, .001 to .20 percentcalcium, .0] to 1.0 percent aluminum, a trace to .50 percent of a rareearth metal, balance essentially iron.

6. An electric resistance element consisting substantially of 35 percentnickel, substantially 20 percent chr0- mium, 001 to .07 percent calcium,.01 to .40 percent aluminum, a trace to .20 percent of a rare earthmetal, balance essentially iron.

7. An electric resistance element consisting substantially of 35 percentnickel, substantially 20 percent chr0- mium, .001 to .20 percentcalcium, .01 to 1.0 percent aluminum, a trace to .50 percent cerium andlanthanum, balance essentially iron.

8. An electric resistance element consisting substantially 0f 35 percentnickel, substantially 20 percent chr0- mium, .001 to .07 percentcalcium, .01 to .40 percent aluminum, a trace to .20 percent cerium andlanthanum, balance essentially iron.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS 1,941,648 Armstrong Jan. 2, 1934 2,047,916 LohrJuly 14, 1936 2,047,917 Lohr July 14, 1936 2,047,918 Lohr July 14, 19362,581,420 Lohr Jan. 8, 1952 FOREIGN PATENTS 488,926 Great Britain July12, 1938

